<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      #canvas {
        border: 1px solid;
      }
    </style>
  </head>

  <body>
    <canvas width="400" height="400" id="canvas"> 请升级你的服务器 </canvas>
    <script>
      var canvas = document.querySelector("#canvas");
      var context = canvas.getContext("2d");
      context.setLineDash([10, 10]);
      context.lineDashOffset = 0;
      context.strokeStyle = "#000";
      var offset = 0;
      setInterval(() => {
        context.clearRect(0, 0, 400, 400);
        offset += 0.5;
        if (offset >= 20) {
          offset = 0;
        }
        context.lineDashOffset = offset;
        context.strokeRect(50, 50, 100, 100);
      }, 16.7);
    </script>
  </body>
</html>
